1. Field of the Invention
The present invention relates to a corneal surgery apparatus which ablates a cornea to change a surface shape of the cornea.
2. Description of Related Art
Conventionally, there is known a corneal surgery apparatus which ablates a cornea by irradiation of a laser beam and changes a surface shape of the cornea to correct a refractive error of an eye. In this kind of surgery, characteristics such as a corneal shape and eye refractive power distribution (or distribution of wave aberration) of a pre-operative patient's eye (eye to be operated on) are measured, and data on corneal ablation is obtained based on the measurement data.
A position (attitude) of the patient at the time of the measurement for obtaining the data on the corneal ablation is generally sitting or standing (a state where the patient's eye faces forward). On the other hand, a position (attitude) of the patient at the time of the corneal surgery is generally lying on his/her back (a state where the patient's eye faces upward). It is known that, in the case of the eye which faces upward contrary to the eye which faces forward, torsion (rotation) of an eyeball occurs. Therefore, there is proposed an optical system for adjusting a condition of the eyeball, which differs at the time of the measurement before the surgery and at the time of the surgery, utilizing an iris image of the eye.
However, during the laser irradiation, or in LASIK surgery (Laser in Situ Keratomileusis) in which an epithelium is incised into a layer to form a corneal flap and then the laser irradiation is performed, the iris image is difficult to obtain since the corneal surface becomes rough. In this case, the torsion information itself on the eyeball is not obtained, or even if obtained, its accuracy gets worse. In addition, also in the case of obtaining positional information on the eye utilizing the iris image, same problems are presented.